Optical triangulation systems are coming into greater use for machine vision for automated inspection, material handling, assembly, and a variety of manufacturing tasks. The precision of these measurement systems relies on the accuracy of calibration and the ability of the system to retain the calibrated accuracy. It has thus become important to devise methods for rapid and accurate calibration of three-dimensional sensors. See for example, U.S. Pat. No. 4,682,894.
The manufacture of precision calibration equipment is potentially expensive because of the difficulty in obtaining the necessary accuracy. The cost can best be reduced by using the simplest shapes, minimum number of parts, and using inherently accurate machining procedures.
The accuracy of calibration of optical sensors is affected by dependencies on calibration techniques which rely on results obtained from calibrating sensor depth. Plate flatness measured to +/-0.0001" and precise translation mechanisms permit relatively easy calibration of optical sensors with accuracies up to +/-0.001".
Surface reflectivity variations caused by surface attitude as well as reflection coefficients and specularity adversely affect calibration accuracy. Flat, matte surfaces reduce inaccuracy best from these causes.
In the prior art it was shown that by taking a flat plate perpendicular to the centerline of an optical measurement sensor, and by accurately translating along that centerline and recording measurements made at specific intervals, one would be able to calibrate the sensor very accurately. This procedure, however, has turned out to be very restrictive in some applications.
It was also shown in the prior art that measurements lateral to the centerline of the sensor could be made by sloping the plate at a known angle to the centerline of the sensor, and translating the sloped plate either along the centerline or orthogonal to it.